Instead of chemicals conventionally used in finishing processes in textile, selection of chemicals having lower environmental impacts and also optimization of processes is needed and studies have been carried out in this line.
Ozone gas is used in bleaching as well as bleacher and color bleacher in parts washing processes of garments made from denim in recent years as ozone gas is a very strong bleacher in addition to its bactericide and fungicide feature.
Being an oxidative agent and an active oxygen source, Ozone has become an alternative to potassium permanganate, hypochlorite and hydrogen peroxide in processes of bleaching cotton fabrics and products. Ozone has advantage over other bleaching chemicals in finishing processes due to its features of not releasing residuals, not damaging environment and being efficient even at low temperatures.
In textile processes where ozone is used, ozone generator can produce ozone from air, and ozone shows a strong oxidative feature and is efficient at low temperature, it may not require addition of auxiliary chemicals and may provide saving in heating costs just because it is highly efficient at cold temperatures.
Ozone gas is generally used in small scale of denim washing processes for removal of dye and cleaning pocket back staining for the purpose of used effect and creation of patterns in denim washing sector.
Successful color fading by ozone is subject to fulfillment of some conditions. Firstly, the textile should be wet so that ozone may react with the dyes of textile products. System is preferred to have a given level of moisture during process. In addition, ambient temperature is to be kept substantially constant for a repeatable finishing result in ozonation process.
The moisture required for ozonising textile products with current ozonation systems is provided by means of directly wetting the textile products and/or putting wet fabric parts other than textile products. However, wetting fabric completely in line with these methods causes swelling of yarns in the fabric. This effect enhances surface area of yarn on fabric surface and supports ozone diffusion while ozone movement capacity is restricted in deeper parts of the fabric. Therefore, penetration of ozone into fabric reduces and ozonation performance decreases.
The document numbered EP0554648B1 discloses decolorizing a textile material containing cellulosic material having warp yarn with use of ozone. Said garment is dyed with an ozone oxidizable dye, said garment is wetted and then said garment is contacted in a vapour phase with a mixture of steam and ozone at high temperatures for a selected period of time. Here steam represents inert gases. Upon contacting steam, ozone oxidizes said dye and the oxidation with the ozone is terminated prior to any substantial oxidation of the warp yarn of the cellulosic material. Moisture textile material needing for ozonizing under this patent certificate is provided by means of heating the textile material.
PCT application numbered WO2014113238 discloses use of a dry ozonising process to decolorize a dyed denim fabric. With use of ozone, the application aims to eliminate disadvantages caused by stone washing method and use of bleaching chemicals. General and/or local decolorizing is provided in denim fabrics by means of applying three different methods containing use of ozone. In the first method, denim fabric is wetted, excess amount of water is removed and the fabric is subjected to ozone for decolorizing. In the second method, water is sprayed on to the area of denim desired to be decolorized and the fabric is exposed to ozone. In the third method, denim textile product and wet cotton fabric craps are put into a drum together and all drum content is exposed to ozone. Said three methods can be applied separately as well as in a combination. In the application, the moisture needed for ozonizing is provided by wetting the main fabric and/or putting wetted cotton scraps together with main fabric into the drum. In this application, for decolorizing regionally on the fabric, it is sprayed onto desired area.